https://github.com/llvmbot created
https://github.com/llvm/llvm-project/pull/100149
Backport d0ca9f2
Requested by: @ldionne
>From c264db19ef5ac5de02596ebb8ff3774394c871b4 Mon Sep 17 00:00:00 2001
From: Mark de Wever <ko...@xs4all.nl>
Date: Tue, 23 Jul 2024 18:13:22 +0200
Subject: [PATCH] [libc++][string] Fixes shrink_to_fit. (#97961)
This ensures that shrink_to_fit does not increase the allocated size.
Partly addresses #95161
(cherry picked from commit d0ca9f23e8f25b0509c3ff34ed215508b39ea6e7)
---
libcxx/include/string | 17 ++++++--
.../string.capacity/shrink_to_fit.pass.cpp | 41 +++++++++++++++++++
2 files changed, 55 insertions(+), 3 deletions(-)
diff --git a/libcxx/include/string b/libcxx/include/string
index ba86a32090825..9fa979e3a5178 100644
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -3358,23 +3358,34 @@ basic_string<_CharT, _Traits,
_Allocator>::__shrink_or_extend(size_type __target
__p = __get_long_pointer();
} else {
if (__target_capacity > __cap) {
+ // Extend
+ // - called from reserve should propagate the exception thrown.
auto __allocation = std::__allocate_at_least(__alloc(),
__target_capacity + 1);
__new_data = __allocation.ptr;
__target_capacity = __allocation.count - 1;
} else {
+ // Shrink
+ // - called from shrink_to_fit should not throw.
+ // - called from reserve may throw but is not required to.
#ifndef _LIBCPP_HAS_NO_EXCEPTIONS
try {
#endif // _LIBCPP_HAS_NO_EXCEPTIONS
auto __allocation = std::__allocate_at_least(__alloc(),
__target_capacity + 1);
+
+ // The Standard mandates shrink_to_fit() does not increase the
capacity.
+ // With equal capacity keep the existing buffer. This avoids extra work
+ // due to swapping the elements.
+ if (__allocation.count - 1 > __target_capacity) {
+ __alloc_traits::deallocate(__alloc(), __allocation.ptr,
__allocation.count);
+ __annotate_new(__sz); // Undoes the __annotate_delete()
+ return;
+ }
__new_data = __allocation.ptr;
__target_capacity = __allocation.count - 1;
#ifndef _LIBCPP_HAS_NO_EXCEPTIONS
} catch (...) {
return;
}
-#else // _LIBCPP_HAS_NO_EXCEPTIONS
- if (__new_data == nullptr)
- return;
#endif // _LIBCPP_HAS_NO_EXCEPTIONS
}
__begin_lifetime(__new_data, __target_capacity + 1);
diff --git
a/libcxx/test/std/strings/basic.string/string.capacity/shrink_to_fit.pass.cpp
b/libcxx/test/std/strings/basic.string/string.capacity/shrink_to_fit.pass.cpp
index 057050cdcf7fa..6f5e43d1341f5 100644
---
a/libcxx/test/std/strings/basic.string/string.capacity/shrink_to_fit.pass.cpp
+++
b/libcxx/test/std/strings/basic.string/string.capacity/shrink_to_fit.pass.cpp
@@ -63,8 +63,49 @@ TEST_CONSTEXPR_CXX20 bool test() {
return true;
}
+#if TEST_STD_VER >= 23
+std::size_t min_bytes = 1000;
+
+template <typename T>
+struct increasing_allocator {
+ using value_type = T;
+ increasing_allocator() = default;
+ template <typename U>
+ increasing_allocator(const increasing_allocator<U>&) noexcept {}
+ std::allocation_result<T*> allocate_at_least(std::size_t n) {
+ std::size_t allocation_amount = n * sizeof(T);
+ if (allocation_amount < min_bytes)
+ allocation_amount = min_bytes;
+ min_bytes += 1000;
+ return {static_cast<T*>(::operator new(allocation_amount)),
allocation_amount / sizeof(T)};
+ }
+ T* allocate(std::size_t n) { return allocate_at_least(n).ptr; }
+ void deallocate(T* p, std::size_t) noexcept { ::operator
delete(static_cast<void*>(p)); }
+};
+
+template <typename T, typename U>
+bool operator==(increasing_allocator<T>, increasing_allocator<U>) {
+ return true;
+}
+
+// https://github.com/llvm/llvm-project/issues/95161
+void test_increasing_allocator() {
+ std::basic_string<char, std::char_traits<char>, increasing_allocator<char>>
s{
+ "String does not fit in the internal buffer"};
+ std::size_t capacity = s.capacity();
+ std::size_t size = s.size();
+ s.shrink_to_fit();
+ assert(s.capacity() <= capacity);
+ assert(s.size() == size);
+ LIBCPP_ASSERT(is_string_asan_correct(s));
+}
+#endif // TEST_STD_VER >= 23
+
int main(int, char**) {
test();
+#if TEST_STD_VER >= 23
+ test_increasing_allocator();
+#endif
#if TEST_STD_VER > 17
static_assert(test());
#endif
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